Health authorities in the United States are continuing to investigate a widespread outbreak of cyclosporiasis, a foodborne illness caused by the microscopic parasite Cyclospora cayetanensis. The outbreak has attracted significant attention because many patients have reported experiencing severe watery diarrhoea, commonly described as “explosive” diarrhoea, and because investigators have yet to identify a single confirmed source of contamination.
According to the U.S. Centers for Disease Control and Prevention (CDC), cyclosporiasis occurs when people consume food or water contaminated with the Cyclospora parasite. Unlike many common gastrointestinal illnesses, the infection is not typically spread directly from one person to another. This is because the parasite requires several days or even weeks outside the human body before it becomes infectious, making contaminated food and water the primary routes of transmission.
The outbreak has been reported across multiple states, with Michigan recording the highest number of cases. As of mid-July 2026, Michigan health officials had documented more than 2,600 infections, while the CDC had confirmed hundreds of additional cases across at least 31 states. Public health experts note that these figures may continue to rise as more cases are identified and reported through surveillance systems. Although investigators believe contaminated leafy greens, particularly lettuce, are the most likely source of the Michigan outbreak, they have not identified a specific farm, grower, supplier or brand responsible for the infections. The investigation involves the CDC, the U.S. Food and Drug Administration (FDA), and state and local health departments, which are working together to trace the contaminated food through distribution networks.
Identifying the source of a Cyclospora outbreak can be particularly difficult. Symptoms generally appear about one week after exposure but can take up to two weeks to develop. By the time people become ill, they often find it difficult to remember everything they consumed in the days before symptoms began. Fresh produce also moves through multiple farms, packing facilities, distributors, wholesalers and retailers before reaching consumers, making it challenging for investigators to pinpoint exactly where contamination occurred.
The symptoms of cyclosporiasis can be severe and prolonged. The most common symptom is frequent watery diarrhoea, but patients may also experience abdominal cramps, nausea, fatigue, loss of appetite, bloating, increased gas, weight loss and, in some cases, vomiting or a low-grade fever. Without treatment, the illness can last for several weeks or even longer. Some people experience recurring symptoms that improve before returning again. While most healthy individuals recover fully, the illness can lead to significant dehydration, particularly among young children, older adults and people with weakened immune systems. Severe dehydration may require hospital treatment, making early medical attention important for individuals with persistent diarrhoea.
Unlike viral stomach illnesses such as norovirus, cyclosporiasis can usually be treated with antibiotics. The recommended treatment is trimethoprim-sulfamethoxazole (TMP-SMX), which helps eliminate the parasite and shortens the duration of illness. Diagnosis typically requires specialised laboratory testing because Cyclospora is not always detected through routine stool examinations. Healthcare providers may need to specifically request testing for the parasite when symptoms and patient history suggest cyclosporiasis. Health officials continue to encourage consumers to follow safe food-handling practices. Fresh fruits and vegetables should be washed thoroughly before consumption, although experts note that washing alone may not completely remove the parasite. Discarding the outer leaves of lettuce, maintaining good hand hygiene during food preparation and ensuring access to safe drinking water are additional measures that may help reduce the risk of infection.
Cyclospora outbreaks have occurred in the United States before. Previous investigations have linked infections to imported basil, cilantro, raspberries, snow peas and bagged salad mixes. Because contamination often occurs before produce reaches retailers, identifying the exact source has historically been a complex and time-consuming process.
The current investigation remains ongoing, and health authorities have not issued a nationwide recall linked to a confirmed product. Officials continue to analyse patient interviews, laboratory results and food distribution records in an effort to identify the contaminated source and prevent further infections. Until that source is confirmed, public health agencies are urging consumers to remain aware of food safety practices and seek medical care if they experience persistent diarrhoea after eating fresh produce.
